The second effect of the 5e feat "Shield Master" reads (emphasis mine):
If you aren't incapacitated, you can add your shield's AC bonus to any Dexterity saving throw you make against a spell or other harmful effect that targets only you.
The wording here is ambiguous. Does the bolded text only apply to the "or other harmful effect" part, or does it apply to the "a spell or other harmful effect" part? Applying the first reading leads to many scenarios that are logically questionable, but fully plausible under action-movie physics (hiding behind a big shield to avoid the AoE of a fireball), and some scenarios that are absurd (like ducking behind your shield to avoid a Lightning Bolt, a spell that explicitly travels through all creatures and many obstacles).
On the other hand, applying the second reading removes almost all utility from this portion of the feat. IMO, the rest of the feat alone isn't worth the ASI trade-off for the vast majority of characters. Off-hand, I can't think of any single target spells that offer a DEX save. Is there an official ruling on which reading of the feat is correct?